Plastic container



PLASTIC CONTAINER Filed Aug. 30, 1963 INVENTOR RANDOLPH D. Luma BY a9 1. 2% M ATTORNEYS United States Patent 3,248,000 PLASTIC CONTAINERRandolph D. Lurie, Park Forest, Ill., assignor to Continental CanCompany, Inc., New York, N.Y., a corporation of New York Filed Aug. 30,1963, Ser. No. 305,804 3 Claims. (Cl. 220-72) This invention relates toa novel method of and apparatus for deep-drawing plastic. containerbodies possessing high dimensional stability and excellent end seamingcharacteristics by subjecting a flange of a drawn container body to aforce which balances internal stresses set up in the flange by priordrawing and redrawing operations.

Independent of the final shape of a deep-drawn article, such as acontainer body, a conventional deep-drawing process might generallyconsist of three basic operations.

The first operation performs the combined function of cutting a blank ofsuitable material, such as plastic, to proper size and drawing'thisblank into a shallow container body. A flat sheet of plastic material isplaced between upper and lower portions of a die assembly and theplastic material is clamped between a draw punch and a draw ring of thedie assembly. Simultaneously, with this clamping action the plasticmaterial is trimmed into a blank by the cutting action of the draw punchwhich forces the plastic material passed a shear fitting closely aroundthe outside of the draw punch, thus causing the plastic material to becut cleanly and uniformly.

The portion of the blank whichforms the container wall is drawn from thematerial which is clamped between the draw punch and the draw ring. Thedownward progress of the draw punch and the draw ring causes thismaterial to be drawn into a narrow space between the draw punch and adie center pad of the die assembly. The clearance between the draw punchand the die center pad determines the wall thickness of the finishedcontainer body. At the completion of this first operation, the containerbody is withdrawn from the die assembly for subsequent operations. Atthis time the container body comprises a generally shallow containerwall which may terminate in a flange formed from the material clampedbetween the draw punch and the draw ring.

The second operation performs the function of converting the shallowcontainer body to a container body of greater depth and smallerdiameter. The second operation redraws, to a greater depth, thecontainer body which has already been formed.

In this second operation, the shallow container body is placed over adraw ring and die center pad of another die assembly.

The portion of the plastic material which is to form the wall of theredrawn container body is drawn from the plastic material clampedbetween the draw punch and the draw ring, and that material extendingoutside the die not clamped between the draw punch and draw ring. Duringthe progress of the redrawing operation, as the draw punch is forceddownwardly pushing the draw ring ahead of it, material is drawn from theclamped material between the draw punch and the draw ring into the spacebetween the draw punch and the die center pad, thus forming the wall ofthe redrawn container body. As material is drawn from between the drawpunch and the draw ring, new material is drawn from outside the drawring into this clamped area to replace the material which has beenremoved. This new material drawn into the clamping area of the drawpunch and the draw ring comes from that material which had been used toform the container wall during the first operation.

. force.

This process usually continues until all of the material outside of thedraw ring has been drawn into the area between the draw punch and thedraw ring.

At the completion of this second redrawing operation not all of theplastic material has been drawn into the space betwen the draw punch andthe die center pad, and a flange remains around an open mouth of theredrawn container body. This is the flange to which an end or closure issubsequently attached by a seaming operation.

For all practical considerations, the flange material is virtuallyidentical to the original sheet material prior to the first operation.However, in the absence of ideal or theoretical material flow during thedrawing or redrawing operations, the bending of the plastic material toform the radius between the container wall and the flange sets upundesirable internal stresses in the plastic material. That is, thebending of any solid body causes the material at the inside of the bendto be put into compression and the material on the outside of the bendto be put into tension. The net result of this is that the bend ends tostraighten out after the applied bending forces have been removed. Thisapplies to the radius of the container body during the drawing andredrawing operations. The inside of the radius is subjected tocompression stresses while the outside of the radius is placed under theinfluence of tension stresses. These tension and compression stresses donot generally compensate one another with the result that the stressesin the flange of the redrawn container cause the plastic materialtocreep i-f unrestrained by some balancing The radius tends to straightenout due to this creep and the desired angle of the flange with respectto the container wall (generally degrees) cannot be maintained.

These unbalanced forces or stresses in the flange also tend to increasethe plug diameter of the container mouth. This makes it virtuallyimpossible to scam or otherwise secure a metallic end or closure to thedeformed plastic flange of the container body.

Heretofore, the container manufacturing industry had failed to recognizeand solve the inherent structural deficiencies in the flange ofdeep-drawn container bodies. The novel invention herein disclosed solvesthe problems inherent in conventional plastic container bodies and theflanges thereof in an unobvious manner by a third drawing operationwhich essentially performs two functions.

First, the flange at the open mouth of the redrawn container body isshaped to a proper contour by a die assembly which simultaneouslysubjects the flange adjacent the radius of the container wall to a forcewhich balances the internal stresses thereof, and secondly, the flangeis trimmed to the exact dimensions required for a desired metallic endor closure after these forces have been balanced. In effect, the redrawncontainer body is placed into a female die of a die assembly which isclosed to complete the shaping of the flange. During this operationthere is no drawing per se, but rather, the material of the flangeadjacent the radius is subjected to controlled flow by the applicationof pressure thereto. The flowing of the plastic material of the flangeis accomplished by an upstanding annular ridge of the female die whichopposes a planar annular wall of a male die. As the male and female diesforceably close against upper and lower surfaces of the flange of thecontainer body, the annular ridge coins the lower surface or undersideof the flange setting up compressive forces therein which balance andcompensate the internal tensile stresses in the area of the radius ofthe flange. This coining preserves the bending angle of the radius bybalancing the internal forces of the radius and prevents the flange fromrapidly For example a conventional plastic flange is not very rigid .dueto its tendency to straighten out after the completion of the thirddrawing operation heretofore de-. scribed and a metal end or closurewhich is being conventionally double seamed to this flange easily pushesthe plastic material aside so that a poor seam or no seam 18 formed. Thenovel coined flange of this invention increase the rigidity of theflange so that the plastic material thereof is not pushed out ofposition by the metal end or closure during the course of a conventionaldoublesea-ming operation.

After the coining action is completed no change in the plug diameter ofthe container body can take place. Thus, by trimming the containerflange after the flange has been coined, variations in dimensions fromcontainer body to container body which wouldotherwise occur areeliminated since the trimming occurs only after all of the internalforces in the flange have been balanced. All of the container bodydimensions can be consistently held to close tolerances from containerbody to container body and the dimensional stability of the flangesthereof is insured. It is therefore an object of this invention toprovide a novel method of an apparatus for forming a container body by adeep-drawing operation which increases the dimensional stability andend-seaming characteristics of a flange of the container body bybalancing the internal stresses of the flange which tend to distort theflange in a manner heretofore unprovided for in the prior art.

Another object of this invention is the provision of a novel method offabricating a container body by deepdrawing a container body of the typeincluding a tubular wall integrally joined to a flange possessinginternal tensile stresses tending to cause the material of the flange tocreep and distort, and subjecting the flange to a compressive [force bya coining operation which balances the internal tensile stresses of theflange thereby enhancing the dimensional stability and end seamingcharacteristics of the container body.

Still another object of this invention is to provide a novel method ofproducing a plastic container body by performing a drawing operation toform a container body of the type including a tubular wall integrallyjoined by a radius to a flangepossessing internal tensile stressestending to distort the plastic material of the flange, subjecting theflange adjacent the radius to a compressive force by a coining operationwhich balances the internal tensile stresses of the flange to preventcreep and thereby stabilize the pre-selected dimensions of the containerbody, and thereafter, severing or trimming the flange to accommodate ametallic end or closure which is subsequently united to the can body bya seaming operation.

Another object of this invention is to provide a novel die including apair of relatively reciprocal aligned members, a first of the membersincluding a bore and a second of the members having a projection alignedwith the bore for entry therein upon relative reciprocation of themembers, a substantially planar Wall of the first member being spacedfrom and opposed to a substantially planar wall of the second member,and one of the planar walls including means cooperative with the otherof the planar walls for subjecting a flangeof a container body receivedbetween the walls to a compressive force upon relative reciprocation ofthe pair of members to enhance the dimensional stability and the endseaming characteristics of the container body.

Still another object of this invention is to provide a novel apparatusof the type immediately above-described wherein the means for subjectingthe flange to a compressive force is an annular shoulder projecting fromthe wall of the first member toward the wall of the second member toeffect a coining operation on the flange.

A further object of this invention is to provide a novel apparatus ofthe character immediately above-described, and in addition, to provide ashear externally surrounding and slidably contacting an exterior wall ofthe first member which trims the flange upon reciprocation of the pairof members after the flange has been coined by the annular shoulder.

Another object of this invention is to provide a novel container body ofthe type including a tubular container wall integrally joined by aradius to a flange and including means adjacent the radius for settingthe flange by balanc-.

ing internal forces thereof.

Still another object of this invention is to provide a novel containerbody of the character above-described in which the means for balancingthe internal stresses of the flange tending to distort the same is. acoined groove adjacent the radius of the container body.

With the above, and other objects in view that will hereinafter appear,the nature of the invention will be more clearly understood by referenceto the following (16? tailed description, the appended claims and theseveral views illustrated in the accompanying drawing.

In the drawing:

FIGURE 1 is a fragmentary sectional view of a die assembly andillustrates a redrawn flanged container body received in a bore of afemale die, a male die cooperating with an upwardly directed annularridge of. the female die to coin a flange of the container body adjacenta radius:

thereof, and the position of a shear prior to a trimming operation tosize the flange.

FIGURE 2 is a fragmentary sectional view of the die assembly of FIGURE 1and illustrates the shear completing the removal of the material of theflange pro-.-

jecting radially outwardly beyond peripheral walls of the male andfemale dies.

FIGURE 3 is a fragmentary top perspective view of a container body, andillustrates a relatively shallow indentation or groove formed in aflange of the container body. A novel die assembly constructed in.accordance with this invention is best illustrated in FIGURES 1 and 2of the drawing, and is generally designated by the reference numeral 10.

The die assembly 10 comprises a male member or die 11 and a femalemember or die 12. The male and female dies, 11 and 12 respectively, arearranged in axial alignment and are relatively reciprocally mounted in acon-' ventional press in a manner well known in the prior art.

and forming no part of this novel invention.

T-he'male die 11 includes a draw punch 13. The draw punch 13 is securedto the male die 11 by a plurality of bolts (not shown). An upper bodyportion 14 of the draw punch 13 is substantially circular in transversesection and has an upper exterior peripheral wall 15. A downwardlyfacing substantially planar annular'wall or shoulder 16 of the upperbody portion 14terminatesw radially inwardly at a lower externalperipheral wall 17 the male die 11 and the interior peripheral wall 23there.

of establishes the exterior diameter of container body in a manner whichwill be made apparent hereafter.

A substantially planar, annular, upwardly facing wall 24 of the femaledie 12 opposes the downwardly facing annular wall 16 of the draw punch13. An upwardly projecting circumferential shoulder or ridge is locatedat the juncture of the annular upwardly facing wall 24 and interiorperipheral wall 23 of the female die 12. A pair of upwardly convergingcircumferential wall portions 26 and 27 of the shoulder or ridge 25 setoff a circumferential apex 28 having an included angle of substantially90 degrees.

An upper exterior peripheral wall 30 of the female die 12 is in coplanaralignment with the upper exterior peripheral wall 15 of the draw punch13. The exterior peripheral wall 30 of the female die 12 terminates at agradually downwardly diverging circumferential wall 31.

A shear 32 surrounds the female die 12 and is immovably mounted in thedie assembly 10 in any conventional manner. The shear 32 has adownwardly diverging lower circumferential wall 33 which normally seatsagainst the downwardly diverging circumferential wall 31 of the femaledie 12. An inner circumferential wall 34 of the shear 32 guidablycontacts the exterior peripheral wall 30 of the female die 12. The innercircumferential wall 34 of the shear 32 terminates at a circumferentialshearing or trimming edge 35.

In describing the operation of the die assembly 10, it is to beunderstood that the die assembly 10 is first placed into a conventionalpress (not shown) and thereafter the press is actuated to space the maledie 11 a considerable distance above the female die 12. A conventionalair cushion or a plurality of compression springs acting against theunderside of the female die 12 forces the female die 12 to riseupwardly, as viewed in FIGURE 1 of the drawings, to bring the downwardlydiverging circumferential wall 31 of the female die 12 into abutmentwith the downwardly diverging circumferential wall 33 of the shear 32.

At this time, a plastic container body 36 having a cylindrical wall 37joined to a flange 38 by an integral radius 40 is inserted into thefemale die 12 of the die assembly 10. The container body 36 may beconstructed from polyethylene, polypropylene or similar plasticmaterials, and has already been redrawn in the manner heretoforedescribed. The redrawn container body 36 is therefore under largeinternal stresses, particularly in the area of the flange 38 where anupper surface 41 at the radius 40 is under high internal tensilestresses while an under surface 42 is under internal compressivestresses.

The press is then closed in a conventional manner forcing the punch 18of the male die 11 into an open mouth 43 of the container body 36defined by an uppermost portion of the cylindrical container wall 37. Asthe draw punch 13 carried by the male die 11 descends, the flange 38 ofthe container body 36 is forceably clamped between the opposed walls 16and 24 of the respective male and female dies 11 and 12. This clampingpressure forces the upwardly projecting circumferential ridge 25 of thefemale die 12 into the underside 42 of the flange 38 adjacent the radius40, which causes an indentation 44 to be coined into the under surface42 of the flange 38 completely around the circumferenece of thecontainer body 36, as is best illustrated in FIGURE '3 of the drawing.Since the open mouth 43 of the container body 36 is clamped between thepunch wall 17 and the wall 23 of the bore 22, the coining actionsimultaneously sets the open mouth 43 to the desired tolerance. Inparticular, the inside diameter of the container body, i.e., the plugdiameter is established and the tendency of the open mouth 43 to creepopen causing an undesirable increase in the plug dameter is precluded.This coining by the upwardly projecting circumferential ridge 25compresses the material of the flange 38 and reduces the thicknessthereof approximately ten to twenty percent. During the coining of thecontainer body 36 there is no drawing per se; rather, the plasticmaterial of the container body is forced to flow only by the applicationof pressure between the draw punch 13 and the female die 12.

As the draw punch 13 and the female die 12 are further depressedagainst-the air cushion or compression springs acting against theunderside of the female die, the female die 12' continually movesdownwardly as viewed in FIG- URE 1 against the force of the conventionalair cushion or compression springs. The descent of the female die 12under theinfluence of the male die 11 draws the flange 38 downwardly tothe position illustrated in FIGURE 1 of the drawing. At this point thecutting edge 35 of the shear 32 underlies the under surface 42 of theflange 36. Continued downward movement of the dies 11 and 12 urges theflange 38 of the container body 36 beyond the shearing edge 35 of theshear 32 to the position illustrated in FIGURE 2 of the drawing, therebyshearing or trimming the flange 32 in a manner clearly illustrated inFIG- URE 2. During this shearing operation, it will be particularlynoted that exterior peripheral walls 30. and 15 of the respective dies12 and 11 cooperate with the inner cylindrical surface 34 of the shear32 to evenly trim the flange 38.

It should be particularly noted that the flange 38 of the container body36 is trimmed after the same has been set by the coined indentation 44.This permits very little variation in the contour of successive flangesproduced by the die assembly 10 as compared with flanges which mighthave been trimmed to final dimension before they had been set to thedesired final shape.

After the flange 38 of the container body 36 has been trimmed, the pressis opened in a conventional manner, the container body 36 is removedfrom the female die 12 and the process may again be repeated in themanner described.

A metallic end or closure (not shown) may now be secured to the flange38 of the container body 36 by a conventional double-seaming operation.As heretofore noted, because the coined plastic flange increases therigidity of the flange 38 the plastic material of the flange is notpushed out of position by the metallic closure during the course of theseaming operation. The plug diameter remains substantially constant andbecause undesired creep of the plastic material is avoided, the flange38 thereby virtually eliminating poor seams or no seams at all.

While an example of a preferred form of the die apparatus is disclosedherein, as well as a preferred method and a novel article producedthereby, it is to be understood that variations in the die assembly, themethod and the article may be made without departing from the spirit andscope of this invention. For example, while the die assembly isconstructed to produce a generally cylindrical article or container,this disclosed die assembly is merely exemplary and a die assemblycapable of forming noncylindrical, containers, i.e., oblong,pear-shaped, etc., is within the purview of this application. The novelnon cylindrical containers formed by such a die, as well as the methodof so forming such containers, is also deemed part of this invention. ITherefore, any generally tubular container, either cylindrical ornon-cylindrical, forms a part of this invention and the invention islimited only insofar as defined in the appended claims.

I claim:

1. A drawn plastic article of the type including a tubular wallintegrally joined by an arcuate portion of small radius to a flange, theflange having a first surface, a second opposite surface and apredetermined thickness, the improvement comprising coined groove meansgenerally at the juncture of the arcuate portion and theflange formingan integral part of at least one of said surfaces of said flange, andsaid coined groove means establishing compressive forces in said atleast one surface of said flange which balance tensile forces in theother of said surfaces of said flange thereby neutralizing'the flange toprevent distortion thereof.

2. In a drawn plastic container body of the type including a tubularbody wall integrally joined'by an arcuate portion of small radius to aflange, the flange having an upper surface, a lower surface and apredetermined thickmess, the improvement comprising coined groove meansgenerally at the juncture of the arcuate portion and the fiange formingan integral part of said flange, and said coined groove meansestablishing compressive forces in the lower surface of said flangewhich balance tensile References Cited by the Examiner UNITED STATESPATENTS 6/1947 Da Kin 29-535 4/1952 Foskett 22074 2,887,244 5/1959Betner 22054 2,936,493 5/1960 Scherer 264138 2,979,771 4/1961 Taber18-19 2,989,019 6/1961 Van Sciver 113-51 3,005,572 10/1961 Gustafson etal.. 22072 3,022,758 2/ 1962 Rheingold et a1. 113-46 3,026,573 3/ 1962Ciaio 248138 3,043,354 7/1962 Fitzgerald 22031 3,054,144 '9/1962 Goodwinet a1. 1819 3,104,776 9/1963 Bestrom 22072 3,110,086 11/1963 Phillips29545 3,114,455 12/1963 Claisse et al 20656 FOREIGN PATENTS 129,46010/1948 Australia. 698,124 10/ 1953 Great Britain.

20 LOUIS G. MANCENE,.Pz-imary Examiner.

THERON E. CONDON, GEORGE E. LOWRANCE,

Examiners.

1. A DRAWN PLASTIC ARTICLE OF THE TYPE INCLUDING A TUBULAR WALLINTEGRALLY JOINED BY AN ARCUATE PORTION OF SMALL RADIUS TO A FLANGE, THEFLANGE HAVING A FIRST SURFACE A SECOND OPPOSITE SURFACE AND APREDETERMINED THICKNESS, THE IMPROVEMENT COMPRISING COINED GROOVE MEANSGENERALLY AT THE JUNCTURE OF THE ARCUATE PORTION AND THE FLANGE FORMINGAN INTEGRAL PART OF AT LEAST ONE OF SAID SURFACES OF SAID FLANGE, ANDSAID COINED GROOVE MEANS ESTABLISHING COMPRESSIVE FORCES IN SAID ATLEAST ONE SURFACE OF SAID FLANGE WHICH BALANCE TENSILE FORCES IN THEOTHER OF SAID SURFACES OF SAID FLANGES THEREBY NEUTRALIZING THE FLANGETO PREVENT DISTORTION THEREOF.